1. Field of the Invention
This invention relates to electrophotographic copying technology and in particular to an electrophotographic copying process and apparatus which allows to obtain a uniform image density in multiple reproduction and to speed up the overall copying operation by minimizing the preparatory step of the copying operation as much as possible.
2. Description of the Prior Art
In electrophotographic copying technology, the same photosensitive member is repetitively used, and while the photosensitive member is subjected to the steps of charging, exposing to a light image and discharging, charges such as electrons and holes are captured in the traps present in the photosensitive member to cause the so-called fatigue phenomenon, thereby increasing the capacitance of the photosensitive member. It is disadvantageous when the capacitance of the photosensitive member changes in this manner because it will cause the charging potential on the surface of the photosensitive member to vary, in effect, its sensitivity thereby varying the image density from one copy image to another.
For this reason, various techniques have hitherto been proposed to obviate the problem of fluctuations in image density; however, none of them is satisfactory and they still suffer from disadvantages as described below. First, in accordance with Japanese patent publication No. 49-4337 and Japanese Patent Laid-open No. 53-148444, there is proposed a technique of carrying out pre-exposure of the whole surface of the photosensitive member prior to the charging step in continuous copying operation. In such prior art, however, only the light amount of pre-exposure is controlled in accordance with the degree of fatigue of the photosensitive member in a series of successive copying operations and pre-exposure is always carried out at the beginning of each copying operation in several successive copying operations, so that unnecessary power is expended.
Moreover, Japanese Patent Laid-open No. 55-93188 proposes to limit the idle rotations of a photosensitive drum for the above-described pre-treatment to a single rotation; on the other hand, Japanese Patent Laid-open No. 56-54473 proposes to carry out only light irradiation to a photosensitive member while the apparatus is in a standby state. However, in the former case, there is difficulty in controlling light irradiation at the seam during a single rotation and also in having the whole photosensitive surface fatigued uniformly. The latter case is also disadvantaged in that the fatigue produced only by light irradiation is not necessarily sufficient in preventing the sensitivity of a photosensitive member from fluctuating. Accordingly none of the prior art is satisfactory and there still has been a need for further improvements in a reproduction technique.